Field of the Invention
The present invention relates generally to perforation guns that are used in the oil and gas industry to explosively perforate well casing and underground hydrocarbon bearing formations, and more particularly to an improved apparatus for explosively perforating a well casing and its surrounding underground hydrocarbon bearing formation in a preferred fracturing plane.
Prior Art Background
During a well completion process, a gun string assembly is positioned in an isolated zone in the wellbore casing. The gun string assembly comprises a plurality of perforating guns coupled to each other either through tandems or subs. The perforating gun is then fired, creating holes through the casing and the cement and into the targeted rock. These perforating holes connect the rock holding the oil and gas and the well bore. “During the completion of an oil and/or gas well, it is common to perforate the hydrocarbon containing formation with explosive charges to allow inflow of hydrocarbons to the well bore. These charges are loaded in a perforation gun and are typically shaped charges that produce an explosive formed penetrating jet in a chosen direction” U.S. Pat. No. 7,441,601.
The employment of angled shape charge placement to provide intersecting perforations has generated great interest in recent years. See for example, Triple-Jet™ Perforating System, a paper by Halliburton, Bersas, et al, Perforation on Target, Oilfield Review, and New practices to Enhance Perforating Results, Oilfield Review. (all included in the information Disclosure material of this application). The intersecting perforation assist in cleaning the debris from the perforated channel and are especially useful where there is crushed or loose material adjacent the well bore where the perforation is to be made and in sand formations.
Hydrocarbon fracturing tunnels have certain preferred orientations where the effectiveness of extracting oil/gas is greatest i.e., when a perforation is aligned along the tunnels, oil/gas flows though the perforation tunnels without taking an alternate path that may become a restrictive path creating high tortuosity conditions.
Fractures will initiate and propagate in the preferred fracture plane of the formation. Oriented perforating systems can be used to more closely align a plane of perforation tunnels with a preferred fracture plane. Misalignment between the preferred fracture plane and perforations in a well can result in significant pressure drop due to tortuosity in the flow path near the wellbore. The perforations that are phased at 90 degrees to the preferred fracture plane create pinch points resulting in pressure loss and high tortuosity in the flow path.
Limited entry fracturing is based on the premise that every perforation will be in communication with a hydraulic fracture and will be contributing fluid during the treatment at the pre-determined rate. Therefore, if any perforation does not participate, then the incremental rate per perforation of every other perforation is increased, resulting in higher perforation friction. Therefore, there is a need to angle and space spaced charges to facilitate the limited entry fracturing process to achieve maximum production efficiency.
By design, each perforation in limited entry is expected to be involved in the treatment. If all perforations are involved, and the perforations are shot with 60°, 90°, or 120° phasing, multiple fracture planes may be created, leading to substantial near wellbore friction and difficulty in placing the planned fracturing treatment. Therefore, there is a need for minimal multiple fracture initiations that do not create ineffective fracture planes. Currently, 4 to 8 perforation holes are shot which will reconnect to the predominant fracturing plane during fracturing treatment. Some of the perforation tunnels cause energy and pressure loss during fracturing treatment which reduces the intended pressure in the fracture tunnels. For example, if a 100 bpm fracture fluid is pumped into each fracture zone at 10000 PSI with an intention to fracture each perforation tunnel at 2-3 bpm, most of the energy is lost in ineffective fractures that have higher tortuosity reducing the injection rate per fracture to substantially less than 2-3 bpm. Consequently, the extent of fracture length is significantly reduced resulting in less oil and gas flow during production. Therefore, there is a need for a system to achieve the highest and optimal injection rate per perforation tunnel so that a maximum fracture length is realized. The more energy put through each perforation tunnel, the more fluid travels through the preferred fracturing plane, the further the fracture extends. Ideally, 1000 of feet of fracture length from the wellbore is desired. Therefore, there is a need to get longer extension of fractures which have minimal tortuosity. For example, in order to achieve 2 bpm in each perforation tunnel, a total injection rate of 100 bpm at 1000 psi for 50 perforation tunnels requires 12 clusters each with 4 charges. Therefore, there is a need to shoot more zones with 4 perforating holes in each cluster that are oriented 2 up and 2 down. There is also a need for a swivel/gimbal system to orient the charges in the desired direction to interest at the preferred fracturing plane.
There is a need for the fracture to initiate at the top and bottom first that has the least principal stress so that there is enough flow rates to propagate the fracture. There is a need for a perforating gun that perforates such that the fracture permeates radially to the direction of the wellbore.
Prior art U.S. Pat. No. 8,327,746 discloses a wellbore perforating device. In one example, a wellbore perforating device includes a plurality of shaped charges and a holder that holds the plurality of shaped charges so that upon detonation the charges intersect a common plane extending transversely to the holder. However, there is a need to fracture intersecting jets into a preferred fracturing plane so that a fracture initiates and propagates transversely into a hydrocarbon formation.
Prior art U.S. Pat. No. 8,127,848A discloses a method of perforating a wellbore by forming a perforation that is aligned with a reservoir characteristic, such as direction of maximum stress, lines of constant formation properties, and the formation dip. The wellbore can be perforated using a perforating system employing a shaped charge, a mechanical device, or a high pressure fluid. The perforating system can be aligned by asymmetric weights, a motor, or manipulation from the wellbore surface. However, there is a need for fracturing upwardly and downwardly to create preferred fracture initiation point at select lengths in the preferred fracturing plane.
Prior art U.S. Pat. No. 7,913,758A discloses a method for completing an oil and gas well completion is provided. The perforators (10, 11) may be selected from any known or commonly used perforators and are typically deployed in a perforation gun. The perforators are aligned such that the cutting jets (12, 13) and their associated shockwaves converge towards each other such that their interaction causes increased fracturing of the rock strata. The cutting jets may be also be aligned such that the cutting jets are deliberately caused to collide causing further fracturing of the rock strata. In an alternative embodiment of the invention there is provided a shaped charge liner with at least two concave regions, whose geometry is selected such that upon the forced collapse of the liner a plurality of cutting jets is formed which jets are convergent or are capable of colliding in the rock strata. However, there is a need to fracture into a preferred fracture initiation point in a preferred fracture plane.
Prior art U.S. Pat. No. 7,303,017A discloses a perforating gun assembly (60) for creating communication paths for fluid between a formation (64) and a cased wellbore (66) includes a housing (84), a detonator (86) positioned within the housing (84) and a detonating cord (90) operably associated with the detonator (86). The perforating gun assembly (60) also includes one or more substantially axially oriented collections (92, 94, 96, 98) of shaped charges. Each of the shaped charges in the collections (92, 94, 96, 98) is operably associated with the detonating cord (90). In addition, adjacent shaped charges in each collection (92, 94, 96, 98) of shaped charges are oriented to converge toward one another such that upon detonation, the shaped charges in each collection (92, 94, 96, 98) form jets that interact with one another to create perforation cavities in the formation (64). However, there is a need for fracturing upwardly and downwardly into a preferred fracturing plane perpendicular (transverse) to the well bore orientation.